The present invention relates to rechargeable batteries, and more specifically to storing rechargeable batteries for an extended time.
Many portable electronic devices utilize a rechargeable battery to provide power. These devices include computers, cellular telephones, pagers, radios, and the like. While there are many types of rechargeable batteries used today, including nickel cadmium and nickel metal hydride, lithium ion batteries have become a popular choice. Lithium ion batteries are typically smaller, lighter, and a have a higher charge capacity than other popular rechargeable battery types.
Rechargeable batteries may be stored for long periods of time before an initial use potentially resulting in deeply discharging the cell during the storage time. Shipping a battery at a full charge may create a safety problem. A fully-charged battery presents more of a threat of explosion than a half-charged battery. Therefore, batteries are typically only charged a fraction of their full capacity before shipment. For example, a battery may be charged to a level of fifty-percent capacity before leaving the factory. The amount of energy lost between the time when the battery is initially charged before shipment and the first use of the battery can result in the battery being deeply discharged. Even when the battery is not being used within an electronic device, energy is lost due to the internal circuitry contained within the battery. If the battery is discharged too deeply, the life cycle of the battery may be reduced. Potentially, the battery may not be able to store energy if discharged too deeply.
Briefly described, the present invention is directed at providing a system for storing rechargeable batteries. More specifically, the battery pack is placed into a storage sleep-mode before shipment to the user and remains in the storage sleep-mode until the battery pack senses a charge or load that exceeds a predetermined threshold.
According to one aspect of the invention, the battery pack is put in a storage sleep-mode when the cell state is in a usable mode. The usable mode may be set based on the cell voltage.
According to another aspect of the invention, the battery pack is awakened from the storage sleep-mode when a charge or load to the battery pack exceeds a predetermined threshold. The predetermined threshold may be set based on cell characteristics.
According to yet another aspect of the invention, a terminal or other end-user accessible connection is not needed to place the battery pack into the storage sleep-mode.
According to still yet another aspect of the invention, a charging signal is coupled to the cell during normal operation and decoupled when the battery pack is in the storage sleep-mode.